What we eat greatly influences how we function and affects our propensity to get diseases such as obesity and diabetes. A major goal of Biomedical Research is to uncover which nutrients and metabolites affect our physiology on the one hand and, which of our genes mediate the physiological response to these molecules on the other. We have recently developed an innovative interspecies systems biology model of the nematode C. elegans and its bacterial diet to address these questions. We have used this model to uncover bacterially derived micronutrients and metabolites that affect gene expression, development and fertility in the worm, and to identify a C. elegans metabolic regulatory network that mediates the response to bacterial nutrients. The effects of different bacteria (and their molecules) are mediated via the animal's intestine, which functions as both a digestive and endocrine system. In the next project we will more precisely define the genes that are affected by different bacterial diets, as well as by vitamin B12 and propionic acid - molecules that are central mediators of the effects we observed. In addition, we will use systems-level phenotypic assays and genetic interaction screens to link diet-induced gene expression changes to physiological outputs such as altered developmental rate, fertility, and lifespan and the ability t response to propionic acid toxicity. Finally, we will dissect the precise mechanisms by which metabolic networks communicate with gene regulatory networks and vice versa using a set of transcription factors that are involved in mediating the response to nutritional cues.